15. In a classroom experiment, a cord is attached to one wall and stretched taut across the classroom in a straight line and attached to a point on the opposite wall. The cord is 10.2 m long and has a mass of 0.55 kg. A student plucks the cord sending a pulse that travels down the cord and back three times in 3.20 s. a. (2 pts) What is the speed of the wave traveling down the cord? (Hint: Keep it simple. Think about distance and time.) b. (3 pts) What is the tension in the cord? c. (2 pts) The student wants to produce a vibration frequency of the first harmonic of 2.20 Hz on the cord, to what tension must the cord be stretched to achieve this? Assume that when the student pulls on the cord to adjust the tension, the length of the cord does not change